During slaughtering operations in meat packing plants and slaughtering houses, the slaughtered animals are bled and the blood accumulated. Previously, the blood could be disposed of in sewers or other disposal means used. Current emphasis on environmental quality and particularly controls on industrial waste emissions have foreclosed many prior means utilized for blood disposal.
It is known that the blood resulting from the slaughter of animals, when coagulated and dried, provides a product with protein in high concentration so, with the advent of controls on the disposal of blood, drying animal blood for recovery of protein becomes economically feasible. The protein is relatively stable so the blood can be coagulated and dried at any temperatures below the decomposition temperature of the blood and, specifically, the blood can safely be exposed to the range of temperatures provided by low pressure steam.
Various devices have previously been provided expressly for drying blood. One such device as shown in U.S. Pat. No. 3,431,118 Macy et al, has included a screw conveyor mechanism in an inclined housing. However, the Macy reference relies on the use of live steam injected into the chamber where the blood is coagulated, but not dried and greatly increases the off-gas from the process. Since environmental regulations apply to vapor emissions as well as liquid emissions, the use of devices in accordance with Macy where live steam is injected would further complicate the circumstances surrounding disposal of the blood. The Macy process further requires drying and separation to provide a solid high protein product.
Another method for recovery of albumin or protein from animal blood is shown in U.S. Pat. No. 1,632,321 Sternberg, where a process including mechanical separation of the blood solids, for example by filtration, followed by drying and attrition of the products is disclosed.
None of the known processes for converting animal blood to a solid high protein product permits continuous conversion in a one-step process.